Various types of turbomachines are known, and generally include rotor blades mounted on a rotor that is rotatable within a stationary casing or housing. A particular example of a turbomachine is a gas turbine engine, such as an aircraft engine, which typically includes a combustion chamber, at least one compressor, and at least one turbine. Each compressor and each turbine of the gas turbine apparatus or turbomachine includes a set of running vanes or rotor blades that are rotatable together with the rotor, as well as a set of stationary guide vanes or stator blades that are secured to the stationary casing or housing of the turbomachine. The rotor rotates together with the rotor blades relative to the stationary housing and the stationary stator blades, whereby circumferentially extending gaps are formed between the rotor and the stator, to allow clearance and thereby avoid grazing or collision between the rotor and the stator. For example, respective gaps are formed radially between the rotor and the radially inner ends of the stationary stator blades, and radially between the stationary housing and the radially outer ends of the rotating rotor blades. In order to minimize gas leakage past the rotor blades or stator blades through these gaps, and thereby to optimize the efficiency of the gas turbine apparatus, these gaps must be maintained as small as possible while avoiding grazing or collision of the relatively moving components. Also, various seal arrangements are typically provided in the gaps.
During operation, gas turbines are subjected to considerable mechanical loads, which can lead to a deformation of the housing of the compressor or the turbine out of its nominal circular sectional shape to an oval, oblong, generally square or polygonal, or other non-circular deformed shape. Such deformations can include temporary short-lived deformations that may be vibrational, cyclical, non-cyclical or non-repeating. Such deformations may also include relatively long-duration or on-going deformations. For example, with regard to an aircraft engine, various such deformations are caused, among other things, by the particular installation situation of the engine suspension, and through external forces being applied to the engine or its suspension, for example as a result of flight maneuver loads. Especially in the case of a single-walled housing for the compressor and the turbine, these deformations of the housing directly cause deformations of the inner housing wall surface, thus directly giving rise to deformations of the clearance gaps that are to be sealed between the rotor and the stator.
In order to counteract or reduce the influence of such deformation effects, according to the prior art, the housing of the compressor and the turbine is thickened, stiffened, or otherwise strengthened to resist the deformation, which, however, leads to an increased weight of the gas turbine apparatus. Moreover, due to such a stronger and heavier housing of the gas turbine apparatus, the costs are increased and the operating efficiency of the gas turbine is decreased. These disadvantages are especially significant for an aircraft engine.